In a general process of producing a lipped or flanged container made of paperboard, it is a practice to make pre-cuts paperboard such that the directions of pulp fiber are substantially perpendicular to the circumferential direction of the container's body thereby to increase expandability in the body's circumferential direction in order not to cause buckling or break of pulp fiber in curling a flange. The technique of JPA-52-139577 is among such conventional techniques pertinent to production of paperboard containers.
To increase expandability in the circumferential direction of the container's body is effective for curling finish of the container's opening portion but unavoidably results in reduction of strength against grasping in the body's circumferential direction. As a result, the container's body is easily deformed when the container's body is grasped. Where, in particular, the method is applied to a container in which hot water is poured for cooking, such as a cup of an instant noodle, the container is so soft and inconvenient to grasp.
On the other hand, pulp molded articles have been attracting attention in the light of the resources and environmental issues. Pulp molded articles, having fibers oriented randomly, show smaller difference in elastic modulus depending on fiber orientation than traditional paperboard. However, when the opening portion of a dried molded article is curved as such, it easily suffers from buckling, wrinkling, break of pulp fiber (partial break of a container), and the like.
Accordingly, an object of the present invention is to provide a method of producing a lipped molded article which makes it possible to produce a molded article without involving wrinkling, buckling, break of pulp fiber, and the like in curling a flange.